Media temperature measurement for adjusting the light source in heat-assisted magnetic recording device

Abstract

Apparatus and method for heat assisted magnetic recording (HAMR). In some embodiments, a write element has a magnetic write coil that writes a magnetic pattern to a recording layer of a data recording surface. A light delivery mechanism imparts heat in the form of electromagnetic energy to the data recording layer during operation of the write element. A radiation detector detects radiation power emitting from the recording layer responsive to the operation of the light delivery mechanism. A control circuit determines a direct temperature of the recording layer responsive to the detected radiation power, and as necessary, adjusts a power input to the light delivery mechanism responsive to the determined temperature. The radiation detector may be an infrared photodetector with a graphene-based detection layer. The photodetector may be disposed between a write pole and a return pole of the write element.

What is claimed is: 
     
       1. An apparatus comprising:
 a write element comprising a magnetic write coil configured to write a magnetic pattern to a recording layer of a data recording surface; 
 a light delivery mechanism configured to impart heat in the form of electromagnetic energy to the data recording layer during operation of the write element, the electromagnetic energy comprising a stream of collated incident light at a first frequency and wavelength; 
 a radiation detector configured to detect radiation power emitting from the recording layer responsive to the operation of the light delivery mechanism, the radiation power comprising a stream of reflected light at a different, second frequency and wavelength; and 
 a control circuit configured to determine a temperature of the recording layer responsive to the detected radiation power and to adjust a power input to the light delivery mechanism responsive to the determined temperature. 
 
     
     
       2. The apparatus of  claim 1 , wherein the radiation detector comprises an infrared photodetector adjacent the magnetic write coil. 
     
     
       3. The apparatus of  claim 2 , wherein the infrared photodetector comprises a detection layer comprising graphene. 
     
     
       4. The apparatus of  claim 1 , wherein the write element comprises a write pole about which the write coil extends, the write pole directing write flux at a first density toward the data recording surface to write the magnetic pattern to a recording layer of the data recording surface, the write element further comprising a return pole to receive the write flux at a smaller second density in a down-track direction from the write pole, and wherein the radiation detector is disposed between the write pole and the return pole in the down-track direction. 
     
     
       5. The apparatus of  claim 1 , wherein the light delivery mechanism comprises a light emitting diode (LED), a waveguide and a near-field transducer (NFT). 
     
     
       6. The apparatus of  claim 1 , wherein the control circuit determines the temperature of the recording layer as a fourth power of the detected radiation power. 
     
     
       7. The apparatus of  claim 1 , wherein the control circuit compares the temperature to a predetermined specified temperature range, decreases an input to a driver circuit that drives a light source to reduce a level of power output by the light source responsive to the temperature being higher than the specified temperature range, and increases an input to the driver circuit to increase a level of power output by the light source responsive to the temperature being lower than the specified temperature range. 
     
     
       8. The apparatus of  claim 1 , characterized as a head-disc interface (HDI) in a data storage device that uses heat assisted magnetic recording (HAMR) to record data to a rotatable magnetic recording disc. 
     
     
       9. The apparatus of  claim 1 , wherein the control circuit is further configured to adjust a power input to at least a selected one of the write coil or a fly height adjustment mechanism responsive to the determined temperature. 
     
     
       10. A data storage device comprising:
 a magnetic data recording medium configured for rotation about a central axis at a selected rotational rate; 
 a data transducer configured to be advanced to different radial locations of a data recording surface of the magnetic data recording medium, the data transducer comprising a write element configured to write a magnetic pattern to the data recording surface, a heat assisted magnetic recording (HAMR) system configured to impart heat in the form of electromagnetic energy to the data recording layer during operation of the write element, and a radiation detector configured to detect radiation power emitted from the recording layer responsive to the operation of the HAMR system, the HAMR system comprising a light emitting diode (LED), a waveguide and a near-field transducer (NFT), the waveguide directing a stream of light from the LED to the NFT for focusing as a light beam upon the data recording surface to raise the temperature of the data recording surface to a level that reaches or exceeds a Curie temperature of the data recording surface, the radiation detector detecting a sequence of photons emitted from the data recording surface adjacent a location at which a magnetic field from the write element establishes the magnetic pattern therein; and 
 a control circuit configured to determine a temperature of the data recording surface adjacent the data transducer responsive to the detected radiation power. 
 
     
     
       11. The data storage device of  claim 10 , wherein the control circuit is further configured to adjust a power input to the LED of the HAMR system responsive to the determined temperature of the data recording surface to bring the temperature of the data recording surface within a predetermined temperature range. 
     
     
       12. The data storage device of  claim 10 , wherein the write element comprises a write pole magnetically coupled to a return pole and a magnetic write coil that surrounds the write pole configured to generate magnetic flux that is directed from an end of the write pole to write the magnetic pattern to the data recording surface responsive to an input sequence of bi-directional write currents, and wherein the radiation detector comprises an infrared photodetector disposed between the write pole and the return pole. 
     
     
       13. The data storage device of  claim 10 , wherein the electromagnetic energy directed to the data recording layer comprises a stream of collated incident light at a first frequency and wavelength, and wherein the radiation power emitting from the recording layer comprises a stream of reflected light at the first frequency and wavelength. 
     
     
       14. A method comprising:
 using a light delivery mechanism to direct incident light upon a data recording layer to increase a temperature of the data recording layer from a base temperature to a peak temperature in relation to a power input supplied to the light delivery mechanism; 
 directing a magnetic field from a write element to write a magnetic pattern to the data recording layer responsive to the operation of the light delivery mechanism; 
 detecting, using an infrared photodetector, a level of radiation power emitted from the recording layer adjacent the magnetic field to determine a direct measurement of an instantaneous measurement of the temperature of the data recording layer at or near the peak temperature, the write pole being arranged between the light delivery mechanism and the infrared photodetector in a downtrack direction so that during rotation of the data recording layer each selected location of the data recording layer is sequentially impinged by the incident light, followed by being impinged by the magnetic field, followed by being exposed to the radiation detector; and 
 adjusting the power input to the light delivery mechanism responsive to the instantaneous measurement of the temperature of the data recording layer. 
 
     
     
       15. The method of  claim 14 , wherein the detecting step comprises using the infrared photodetector to detect the level of radiation power emitted from each selected location of the recording layer, and using a control circuit that derives the direct measurement of the instantaneous temperature as a fourth power of the level of radiation power detected by the infrared photodetector. 
     
     
       16. The method of  claim 14 , wherein the light delivery mechanism of the using step comprises a light emitting diode (LED), a waveguide and a near-field transducer (NFT), and wherein the power input to the light delivery mechanism comprises adjusting an input to a LED driver circuit that provides a power input to the LED. 
     
     
       17. The method of  claim 14 , wherein the write element of the directing step comprises a write pole about which the write coil extends, the write pole directing write flux at a first density toward the data recording layer to write the magnetic pattern, the write element further comprising a return pole magnetically coupled to the write pole to receive the write flux at a smaller second density in a down-track direction from the write pole, and wherein the infrared photodetector is disposed between the write pole and the return pole. 
     
     
       18. The method of  claim 14 , wherein the incident light from the light delivery mechanism comprises a stream of collated incident light at a first frequency and wavelength, and wherein the radiation power detected by the infrared photodetector comprises radiated light at a different, second frequency and wavelength. 
     
     
       19. The method of  claim 14 , wherein the incident light from the light delivery mechanism comprises a stream of collated incident light at a first frequency and wavelength, and wherein the radiation power detected by the infrared photodetector comprises radiated light at the first frequency and wavelength. 
     
     
       20. The data storage device of  claim 10 , wherein the write element is disposed between the HAMR system and the radiation detector in a downtrack direction with respect to the data recording surface so that the radiation detector detects the radiation power after application of the magnetic pattern to the data recording surface.